1. Field of the Invention
Lengths of cloth with synthetic coatings are known. The coating can in principle be applied with powder or pastes. The application and distribution of the synthetic product can be made directly, for example, by sprinkling a powder on the back-cloth, or indirectly by means of an intermediary carrier in the form of an engraved roller or a perforated cylinder. Sprinkling methods have the drawback that the powder is deposited without uniformity due to the effects of electrostatic forces. On the other hand, a method in which the powder is applied to the length of cloth by means of an intermediary carrier in the form of an engraved roller has the advantage of a uniform coating being applied without the presence of the disturbing forces of electrostatic charges.
2. Description of the Prior Art
The application of the material deposited in the recesses of engraved roller to the length of cloth must be done by means of heat. In addition, the length of cloth has to be brought into contact with the engraved roller. Hitherto it has not been possible to handle separately the twofold task of, on the one hand, getting the powder onto the length of cloth through the contact of the engraved transport surface and, on the other, supplying enough heat to the powdery synthetic product for it to develop the necessary adhesive strength to stick to the length of cloth.
Thus in one method the length of cloth had to be heated so high by upstream heat sources that upon contact of the hot length of cloth the powder in the recesses of the engraved and cooled roller adhered instantly to the roller. Another method provides for fusing the powder through the back-cloth in contact with the engraved roller and thus providing an adhesive bond with the backing.
Although the temperature handling actually depends only on the nature of the powder used, which can have a higher or lower melting point, the nature of the back-cloth to be coated plays a complicating role in all hitherto-known coating methods using an intermediate carrier, such as an engraved roller. Thus, the temperature regulation, depending on the method used, is governed by how thick the length of cloth to be treated is, what color it is, what its heat conductivity or permeability to radiation is, what its heat capacity is, and what its chemical nature is.